Characteristics
Reactor hall, thermal beam IH3 |
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Monochromator | |||
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Double focusing – horizontal variable focusing. | |||
crystal | d-spacing (Å) 3.355(nominal) 2.087 1.677(nominal) | λ0 (Å) 1.977(expt.) 1.28 (expt.) 0.989(expt.) | E0 (meV) |
Collimation |
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Soller Collimator α1 = 0.4° Honeycomb Collimator α2 = 0.4°
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Choppers | |
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Background chopper | 5000 rpm max |
Sample | |
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Beam area at the sample depending on the monochromator and honeycomb collimator adjustement | |
Sample chamber | diameter 500 mm, height 550 mm |
Vacuum level in the sample chamber | 10-4 mbar |
Ancillary equipment | Furnace: |
Detectors | |
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PSD Reuter-Stockes 3He multi-tube assembly | |
Available detection area | 2.1 m2 |
Detector arrangement | 128 central tubes: diameter 12.7 mm, length 1118 mm |
Pixel size | Height: 0.43 mm Width: 12.7 mm |
Distances, useful ranges and resolution (approximate values) | |||||||||||
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Monochromator – Fermi chopper | 5540 mm | ||||||||||
Fermi chopper – Sample | 1000 mm | ||||||||||
Sample – Detector Dsd (variable) | 2000-6000 mm |
E0(meV) | Dsd | Energy Transfer E(meV) | Angular and Qel ranges | Resolution | ||
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DE / E0 | DQ (Å-1) | |||||
20.9 meV | 2 m 4 m 6 m | ± 18 ± 14 ± 12 | 1° - 15° 1° - 15° 1° - 9° | 0.05-0.8 Å-1 0.05-0.8 Å-1 0.05-0.5 Å-1 | 3% 2.9% 2.4% | 0.02 |
49.9 meV | 2 m 4 m 6 m | ± 50 ± 45 ± 35 | 1° - 15° 1° - 15° 1° - 9° | 0.09-1.3 Å-1 0.09-1.3 Å-1 0.09-0.8 Å-1 | 3.8% 3% 2.7% | 0.03 |
83.6 meV | 2 m 4 m 6 m | ± 80 ± 70 ± 60 | 1° - 15° 1° -15° 1° - 9° | 0.1-1.7 Å-1 0.1-1.7 Å-1 0.1-1.0 Å-1 | 4.5% 3.2% 3.1% | 0.04 |
** Please ask the instrument responsible for this configuration
Instrument description
Keywords in the design of the BRISP spectrometer were
- Thermal neutron energies: allowing for investigations in systems characterized by sound velocities up to 3000 m/s (three different incident energies between 20 and 80 meV are presently available).
- Easy small-angle access: enabling low-Q spectroscopy with thermal neutrons. Elastic wavevector transfer values Qel as low as 0.03 Å -1 at 20 meV incident energy can be reached. The position of the two-dimensional detector can be adjusted to cover different small-angle ranges between 1° and 15°.
- Time-of-Flight technique: for an efficient data collection allowing also for accurate neutron measurements as a function of external parameters such as temperature, pressure and magnetic field.
- Careful optimization of monochromator-collimators-Fermi chopper: leading to 0.5 meV energy resolution and 0.02 Å-1Q resolution in a typical configuration (20 meV incident energy and 4 m sample-detector distance), along with acceptable counting rates (flux at the sample 104 n s-1 cm-2). For this purpose, innovatory solutions were specially developed for some of the BRISP components.
Main components
- A Soller collimator defining the beam impinging on the monochromator, with a collimation angle of 0.4°
- Two focusing multi-crystal monochromators, PG and Cu(111), that allow for the selection of three incident energies in the range from 20 to 80 meV. Fixed/variable curvatures are adopted in/outside the Brisp vertical scattering plane.
- A disk chopper used for background reduction and selection of the desired monochromator reflection through proper phasing with the Fermi chopper.
- Three honeycomb converging collimators [1] to define the incident beam on the sample with a collimation angle of 0.4°, and to optimize convergence at three detector positions (2, 4, 6 m from the sample). A coarse resolution option is also available, without honeycomb collimator.
- A Fermi chopper producing short neutron pulses which enable the time-of-flight analysis.
- A high-vacuum sample chamber possibly equipped with 1.5-300 K MAXI Orange cryostat (100 mm) and 300-1900 K furnace
- A ~2 m2-area position sensitive gas detector (3He) whose distance from the sample can be varied between 2 and 6 m in order to access the required Q-range. A huge vacuum tank hosts the detector. An elastobore – polyethylene shielding surrounds the vacuum tank to reduce the environmental background.
- The long vacuum line ensures an under-vacuum neutron flight path from the background chopper to the detector.